Improved Passivation Performance of Al₂O₃ Interlayer/SnO_x Thin Films Continuously Grown Through Atomic Layer Deposition

Atomic layer deposition of aluminium oxide thin films is introduced as a passivating tunnelling interlayer between electron-selective Tin oxide contacts and silicon absorbers. The surface recombination velocity and specific contact resistance were investigated as a function of both Al₂O₃(1-5 nm) and SnO_x(10-50 nm) thickness. The thin SiO_x passivation layer grown naturally without HF pre-treatment on substrate enhance the carrier lifetime of the stacks by 10 µs. The thermal history of the Al₂O₃ layers prior to SnO_x deposition, and the thermal history of the completed Al₂O₃/SnO_x stacks were also investigated. When an SiO_x/Al₂O₃ passivating stack was introduced, the carrier lifetime and the implied open circuit voltage increased from 22 μs to 875 μs and from 568 to 637 mV, respectively. The introduction of ultrathin ALD-Al₂O₃ significantly reduced the number of oxidation states that acted as defects. The ALD-SnO_x/ultrathin Al₂O₃ stack is an extremely transparent, highly promising, electron selective contact layer that can be used in the design of future Si heterojunctions, without the need for <i>a</i>-Si passivation layers.